The two devices may be a host and a peripheral device, for example. For the purpose of data communication, the host and the peripheral device can be connected together via a serial interface.
The peripheral device may be based on the Bluetooth standard, for example. The host may be a telecommunication device which operates on the basis of the GSM, UMTS or CDMA standard, for example.
In literature written in the German language, the English term “host” is always used as such and is not translated into German. Hence, the term “host” is retained in the rest of the text in the original.
It is conceivable for system resources provided by the host to be used by the peripheral device too. Thus, by way of example, the system clock, which is typically in a range between 10 and 100 MHz, or a clock for the standby mode, for example the clock timing at 32 768 kHz, or the voltage provided by a voltage supply chip may also be used for the peripheral device.
Since the host and the peripheral device are each autonomous systems, operating states may arise in which just the host or just the peripheral device is active and the respective other device is in a standby mode with just low power consumption.
To be able to use the system resources of the host, the peripheral device must be capable of requesting the necessary system resources from the host using request signalling. However, if the host is in the standby mode at the time at which the system resources are needed, then the peripheral device first needs to signal to the host that the host needs to exit the standby mode in order to be able to receive the request signal from the peripheral device.
In addition, an active state is needed on the part of the host and on the part of the peripheral device when data interchange is intended to take place between the host and the peripheral device via the serial interface. Otherwise, the receiver would not be able to receive the data, since the serial interface is not supplied with voltage in the standby mode.
A known way of “waking up” a respective device using the other device is to provide additional control lines between the two devices in addition to the serial interface via which the data transfer takes place. The control lines can be used by one device to ask the other device to exit the standby mode.
In addition, it is also known practice to transfer a wake-up signal between the two devices via the serial interface. This is a protocol-based option which can be used when at least one reception pin, which is part of the serial interface, has a wake-up function in each of the two devices. The wake-up function is designed such that a device switches from the standby mode to the active mode as soon as a signal is applied to the reception pin with the wake-up function.